An important hypothesis in assessing the toxicity of aquatic pollution to human health is that certain species, many invertebrates, can serve as indicators of mammalian toxicity. An assumption of invertebrate toxicity tests is the mammals and invertebrates have similar detoxification capabilities, yet little is known about detoxification in invertebrates. The proposed research characterizes the capacity of an important aquatic invertebrate to detoxify a variety of chlorinated phenols and compares this detoxification ability to mammals. The enzyme glutathione S-transferase (GST), important in phase II detoxification of chlorinated phenols, will be extracted, purified and characterized from two species of brachionid rotifers. The number of isoforms present, their size and subunit structure will be determined through polyacrylamide gel electrophoresis. The substrate specificity of rotifer GSTs will be examined by comparing enzyme specific activity with four different chlorinated phenol substrates. Modulation of GST expression will be examined by exposing rotifers to sub-lethal concentrations of chlorinated phenols and assaying the inducibility of enzyme activity. The two rotifer species investigated differ substantially in their acute toxicities to chlorinated phenols. The hypothesis that this sensitivity difference is the result of differing GST detoxification capabilities will be tested. The GST detoxification capability of rotifers will be compared to that of mammals which already have an extensive literature. If successful, this project should further validate the use of invertebrate models for assessing the impact of aquatic toxins on human health.